Man sentenced to 38 years in massive 'sextortion' scheme

The US teenager was 15 years old when a modelling agency manager calling herself Courtney Jansgen reached out to him on social media with an enticing offer.

Send me nude photos, the attractive woman said, and I'll get you a US$1000 modelling gig.

The teenager obliged.

It was only after it was too late that he learned the truth about his would-be employer: Courtney Jansgen was in fact Anton Martynenko, a man twice his age from Eagan, Minnesota, preying on his adolescent impulses.

In subsequent message, Martynenko offered the teenager US$300 to perform a sex act. When he refused, the nude images "spread like wildfire" on social media, as reported by the Minneapolis Star Tribune, which covered statements the teen made in court Tuesday.

The ordeal happened in 2012, and the teen was just one victim in a massive "sextortion" scheme prosecutors are calling the largest child pornography case ever handled in Minnesota.

Over four years, prosecutors say, Martynenko posed as young women on social media and duped at least 155 teen boys, most of them high school athletes from the Midwest, into sending him nude photos and videos.

When his victims refused his requests for more - or in some cases, turned down sexual advances - he would share the images online, court records show.

Prosecutors said Martynenko coerced at least three teens into sexual acts with him, and two of them later killed themselves, according to the Star Tribune.

After pleading guilty in January to federal child pornography charges, the 32-year-old on Tuesday was sentenced to 38 years in prison for his crimes.

A judge cut two years from his sentence for cooperating with investigators in an unrelated homicide and child pornography case, according to KMSP.

"We all can now be given freedom from this," the victim said in court, as reported by the Star Tribune.

Federal officials and child advocates have raised alarms about sex-related extortion against children in recent months, saying they've seen a rise in schemes like Martynenko's.

Most target far fewer victims, but they follow a similar pattern: adults posing as youths trick minors into sending them sexually explicit photos or videos, then threaten to post them online unless they send more.

FBI officials say victims tend to be between the ages of 10 and 17, and offenders often approach them on social media and anonymous messaging apps.

Earlier this year, the US Department of Justice conducted a "National Child Exploitation Threat Assessment" that surveyed more than 1000 federal, state, local and tribal investigators and other law enforcement members.

More than 60 per cent of respondents said "online enticement of minors" was on the rise, according to the report.

"Sextortion is by far the most significantly growing threat to children," the US Justice Department said.

In court, Martynenko was tearful and contrite, calling his crimes a "getaway" from depression, the Star Tribune reported.

"I literally couldn't have handled myself any worse than I did," he said. "I'll do anything the rest of my life to make it up."

His defence lawyer had asked the judge for the statutory minimum of 15 years and contended that the nearly four decades he received was a de facto life sentence, according to the Star Tribune.

US attorney Andrew Luger told the paper: "This case highlighted how deeply disturbing the criminal obsession of a man like Martynenko can be. How not only does he steal the innocence of teenage boys but through extortion, threats and physical acts he inflicted unspeakable psychological damage to his victims."

Prosecutors said Martynenko started preying on teenage boys in 2011 and continued until he was charged in November 2015.

During that time, Martynenko was living in a home owned by his mother and was working at a mortgage lending firm in Eagan, the Star Tribune reported.

His plea agreement says he used "decoy" profiles on social media to seduce his victims and distribute naked images of them online.

When investigators raided his house in October 2015, they uncovered a thumb drive with folders of his victims' photos, carefully organised by name, age, school, according to the Star Tribune.

In one instance, prosecutors said, Martynenko claimed to be a woman named Marie Anna who had recently moved from Illinois to Minnesota and was looking to make new friends in the area.

He told one victim he was handsome and convinced him to exchange naked pictures, prosecutors said. When Martynenko demanded more, the victim stopped responding.

About a year later, the victim found out that Martynenko had spread the images on social media, prosecutors said.

In other instances highlighted in his plea agreement, Martynenko, posing as a female, messaged juveniles and threatened to post nude pictures of them unless Martynenko could perform a sex act on them.

Prosecutors said Martynenko later engaged in "sexual activity" with the minors.

Martynenko admitted he distributed sexually explicit pictures of his victims on at least 50 occasions, but prosecutors maintain he did so more than 1000 times, according to the plea agreement.

The victim who spoke in court Tuesday said he was tormented by social media alerts showing Martynenko had tagged him in photos, according to the Star Tribune.

He called Martynenko a "terrible human being who spent years of his life making hundreds of teen boys miserable."

"It's an honour to be able to be here to speak for them," the teenager said of the other victims. "I'm now going to enjoy my time without any fear of another attack. It's good to know that he's going to be unable to do that to us anymore."